This invention relates to a method and system for controlling the rear brakes of a vehicle
During braking of an automotive vehicle, the rear wheels tend to experience a higher slip condition for a given brake torque than the front wheels due to the difference in the normal forces on the front and rear wheels. In order to provide a more balanced braking of the front and rear brakes of a vehicle and to establish desired vehicle braking characteristics and rear wheel braking performance, it is known to proportion the braking forces of the front and rear wheels to establish a desired relationship.
One system establishes a desired braking performance of the vehicle rear wheels by controlling the slip of the rear wheels to be substantially the same as the slip of the front wheels. This is accomplished by controlling the speed of the rear wheels so as to be substantially the same as the speed of the front wheels. By imposing substantial equality in the front and rear wheel speeds, the desired brake proportioning between the front and rear brakes is established.
The braking systems of each of the left and right rear wheel brakes may typically have different output torques for a given brake control command input This imbalance in system gains is caused, for example, by side to side differences in brake wear, wheel brake efficiency and brake actuator efficiency. This gain difference between the left and right wheel brakes may result in variations between left and right rear wheel brake torques. Because of these imbalances, the braking performance of the left and right rear wheels will differ even though there is identical control inputs to the individual left and right rear brake systems.
In a brake system where the rear wheel brakes are each controlled by a respective electric torque motor in response to controlled motor current, the imbalance between the left and right wheel brake performance results in side to side motor current to brake torque imbalances. As a result, a given motor current will result in different braking efforts of the left and right rear wheels and a given rate of change in current in each of the motors will result in different rates of change in the left and right side braking efforts.